62 THE ADDRESSES, LECTURES, ETC., OF 



civil and mechanical engineer to prepare designs suitable for the 

 development of its peculiar qualities. If, in constructing a girder 

 for example, a design were to be adopted that had been worked 

 out for iron, and if all the scantlings were simply reduced in the 

 inverse proportion of the absolute and relative strength of 

 the new material as compared with iron, such a girder would 

 assuredly collapse when the test-weight was applied, for the simple 

 reason that the reduced sectional area of each part, in proportion 

 to its length, would be insufficient to give stiffness. You might as 

 well almost take a design for a wooden structure and carry it out 

 in iron by simply reducing the section of each part. The ad- 

 vantages of using the stronger material become most apparent if 

 applied for instance to large bridges where the principal strain 

 upon each part is produced by the weight of the structure itself, 

 for, supposing that the new material can be safely weighted to 

 double the bearing strain of iron, and that the weight of the 

 structure were reduced by one-half accordingly, there would 

 still remain a large excess of available strength, in consequence of 

 the reduced total weight, and this would justify a further re- 

 duction of the amount of the material employed. In constructing 

 works in foreign parts, the reduced cost of carriage furnishes also 

 a powerful argument in favour of the stronger material, although 

 its first cost per ton might largely exceed that of iron. 



The inquiries of the Royal Coal Commission into the extent and 

 management of our coal fields appear to be re-assuring as regards 

 the danger of their becoming soon exhausted ; nevertheless, the 

 importance of economising these precious deposits in the production 

 of steam power in metallurgical operations and in domestic use can 

 hardly be over-estimated. The calorific power residing in a pound 

 of coal of a given analysis can now be accurately expressed in units 

 of heat, which again are represented by equivalent units of force 

 or of chemical action ; therefore, if we ascertain the consumption 

 of coal of a steam engine or of a furnace employed in metallurgical 

 operations, we are able to tell, by the light of physical science, 

 what proportion of the heat of combustion is utilised and what 

 proportion is lost. Having arrived at this point we can also trace 

 the channels through which loss takes place, and in diminishing 

 these, by judicious improvement, we shall more and more approach 

 those standards of ultimate perfection which we can never reach, 



